This would've been me at one point in my life, due to circumstance at the time.
Nothing was ever good enough that I did, nothing ever valuable or wanted, everything was a failure, including myself.
Oddly enough, that wasn't actually TRUE, but that's whot I was TOLD repeatedly from my parents sooooo yeah, eventually yeu tend to believe such things. It involved breaking down pretty bad for a long time, and retreating mentally from the scene by referring to myself in third person for several years, because it was just easier to cope with everything when it wasn't really happening to "me", but more like a character in a book.
Sadly, I was a nicer person back then. More caring, more interested in bending over backwards to help other people, putting forth my absolute effort into doing my best at everything I did. In large part, due to the way I was treated, I've since become a bit bitter, and don't really care whot other people think quite as much. A negative comment still stings like hell, but it's not crippling like it once was. While I try to help others as much as before, it's not something entitled to everyone anymore either, yeu now have to earn that privilege. I put as much effort into helping yeu as yeu help yeurself; if yeu put all yeur effort into fixing yeur problems, I will be there to double yeur efforts. If yeu can't lift a finger to help yeurself, I won't either, anymore.
This was, unfortunately, a required development for survival. When younger, suicide seemed a very good option quite a few times... honestly the only thing that ever really stopped me, wasn't religion or revenge or anything like that, but the simple acknowledgment that I was going to die eventually anyway, so I was guaranteed to die regardless, and would see whot happened with the afterlife, if there is one, then, but that I only get to see life a single time, so should probably make use of that before it's gone.
In the unhealthy ENTP, the Ne goes into overdrive making wild accusations and coming up with bizarre conspiracy theories, from the simple, such as "everyone hates me", to the more elaborate "9/11 was a hoax"... and then Ti helps out by rationalizing the data and trying to fit it to prove the theory.
When yeu have both the capability of seeing things from a thousand different angles and can link many seemingly unrelated things together, and yeu have the ability to also rationalize data in a very streamlined way to make sense of the chaos yeur mind is coming up with, it can either lead to silly behaviour, such as yesterday when I went on for several minutes to a British friend insisting that polar bears pull our buses like sleds here through the snow, and we keep the elderly and handicapped up front for easier access when it's feeding time. It can also lead to deep profound understandings... obvious errors... and in some cases, deep damage to ones own self by being able to see the negative aspects in every situation, as well as the positive, but only focusing on the negative, no matter how obscure or bizarre it may be.
And considering an ENTP's habit of challenging anyone who tries to help, to prove they're right, most people just give up. Whenever I got stuck in a downward spiral, people would try to help; I'd refute their arguments, rationalize away their compliments, all in the typical need to see if they could hold up their argument or if they were just saying so without proof. Problem is... people are emotional... when they give a compliment, and yeu twist it into a cruelty against yeu instead, rather than explain themselves further, or meet yeu in the debate on yeur terms... they tend to give up. Which only proves yeu were right that they really do hate yeu in yeur mind.
It's not a good place to be in, and requires very specific care to bring one out of it, and it's something that most people aren't understanding of, or not willing to put the effort into fixing. Yeu see the other thread in this subforum of rainne asking how to deal with an ENTP when car shopping... now consider them acting the same aggressive manner and refuting everything when yeu say yeu care about them, or that they aren't a waste of flesh.
Problem then becomes, anything they say that's nice, gets twisted into a horrible insult. Anything insulting they say, may desperately be turned into a "They don't really mean that, they must mean something else", but the insults hold more weight when down like that, and it feels more like trying to desperately hold the walls apart with your bare hands when the walls are closing in like a bad indiana jones knockoff.
It's hard to crawl out of the hole, probably harder than for most people, since nothing good said will help, and really, the only key to defeating such is to have other people who care enough to endure the self defeat and persevere through it, and most people just don't understand or have that patience.
A way I heard something mentioned in a quote once that fits is, well this's loosely based on the quote, I don't remember it word for word, but it basically went "Sometimes, when people push you away, they really want you to leave them alone. Other times, they're just testing you, to see if you're willing to follow them into hell. I think I chose the wrong answer this time."
That's pretty much the mindset there... to see if they will keep trying, to test if they really care, to evaluate how much of whot they're saying is TRUE, and how much they just THINK is true. Yeu can't trust whot people say; people lie to themselves all the time. They lie to others subconsciously, trying to be 'nice'. When yeu are in the depths of despair, anything they say has to be validated, and the validation method clashes with most peoples' standard methods of thought, which generally means yeu just push them away until they don't come back.
I'd lost a close love during a rough part of my life that way even. They just gave up, they couldn't take it anymore, and they stopped caring. Rather than provide support, they just ran with it and encouraged it, and eventually left with saying some very hurtful things. That still hurts to this day, several years later. I understand the situation a little better now, after thinking it through in this post, but it really does still hurt.
If yeu ever know an ENTP that gets like this, the key to their pulling through is to argue back against their attempts to disprove yeur affections or kindness, and to persevere no matter how hard they try to push yeu away. They don't want to be left alone, they want to see how far yeu're willing to keep trying to help them. If they can't find a limit, they'll pull out of it. If they find yeu bend easily and give up after a short time, it's just going to cripple them further.
Anyways, having delt with this personally, that's whot it's like, at least to some degree. There's alot of things I really try not to think about of that time in my life, and I'm not going to cover the majority of it, but I hope that answers yeur question.